The primary goal of this AT project is to consolidate existing information on solar cooking, as well as evaluate materials and design techniques utilized for the construction of popular contemporary models.

Cooking in developing countries is customarily done on open fires using firewood, charcoal, and kerosene. This leads to deforestation in these rural regions as well as causing excessive pollution and significant smoke inhalation.

Solar cookers work on the basic principle of sunlight being converted to thermal energy that is retained and used for outdoor cooking purposes, and have the most positive impact in sunny, fuel-scarce regions of the world. Solar cookers provide a space of hot air, which directly heats the pot and food.

Some alternate uses for solar cookers:

Water pasteurization

To disinfect dry medical supplies

To sanitize utensils

Figure 1: Temperature distribution for cooking with a solar cooker.[1]

Essentially, reflectors in the solar cooker focus sunlight on a dark pot within the solar cooker, which has a tight-fitting lid to contain heat and moisture. A dark pot is used as it absorbs the maximum amount of heat, and allows higher cooking temperatures.

In order to trap heat, isolating the air inside the cooker from the surrounding atmosphere makes an important difference. Using a clear solid, like a plastic bag or a glass cover, will allow light to enter, but once the light is absorbed and converted to heat, a plastic bag or glass cover will trap the heat inside. This allows temperature to reach similar levels on cold and windy days as on hot days. These plastic sheets have an added benefit of blocking any leakages that could potentially seep through and damage the cooker.

Cooking containers and the inside bottom of the cooker should be dark-colored or black. Inside walls should be reflective to reduce radiative heat loss and bounce the light towards the pots and the dark bottom, which is in contact with the dark pots. [2]

A solar cooker can be advisably used when the length of one's shadow on the ground is shorter than that individual's height. This indicates that the sun is high enough in the sky to allow for efficient cooking.

Where:
Ei is the energy input in W
It = total solar energy incident upon plane of the solar air being heated in W/m2
Asc is the surface area of the solar cooker

Energy output from the solar cooker can be found as shown below:

Where:
Eo is the energy output in W
mw is the mass of water in kg
cpw = specific heat of water in J/kgK
Asc is the surface area of the solar cooker
Twi is the initial temperature of the water in K
Twf is the final temperature of the water in K
t is the time in seconds

Panel and box cookers are easily and inexpensively built using corrugated cardboard (carton board) as the form. To increase durability, outer, non-reflective surfaces can be painted, oiled or waxed to help protect from moisture.

• Plain or corrugated plastics
• Wood
• Woven mats

OUTER BOX :
Should be made of materials that are well insulated and can be sealed well with the lid. Several of the following materials will satisfy these requirements:

• Plain or corrugated plastics
• Wood
• Metal
• Masonite
• Bricks

INNER BOX:
Should be able to withstand high temperatures without releasing any fumes. The surface that faces the cooking pot should be reflective, lined with reflective material, or black. Several of the following materials will satisfy these requirements:

Approximately 2,400 square centimeters of scrap aluminum plate will make one 20 cm x 27.5 cm x 5.5 cm pan, with cover. The material cost is less than $0.30 per pan. [9]

This can be used as a reference to construct your own solar cooker with the aluminum plates available locally. The size of the cooker will be dependent on the size of the pan, and the overall unit size is subject to what is most economical in your particular geographic region.

Several Non-Government Organizations (NGO's) and private organizations have taken it upon themselves to promote the benefits of solar cooking in developing rural areas, from creating DIY designs to setting up training camps to educate villagers on how to build and cook with these devices. Some of these groups are listed below: